Normally, the user specifies which device to affect by setting ifr_name to the name of the interface. All other members of the structure may share memory.

Ioctls
If an ioctl is marked as privileged, then using it requires an effective user ID of 0 or the CAP_NET_ADMIN capability. If this is not the case, EPERM will be returned.
SIOCGIFNAME

Given the ifr_ifindex, return the name of the interface in ifr_name. This is the only ioctl which returns its result in ifr_name.

SIOCGIFINDEX

Retrieve the interface index of the interface into ifr_ifindex.

SIOCGIFFLAGS, SIOCSIFFLAGS

Get or set the active flag word of the device. ifr_flags contains a bit mask of the following values:

Setting the active flag word is a privileged operation, but any process may read it.

SIOCGIFPFLAGS, SIOCSIFPFLAGS

Get or set extended (private) flags for the device. ifr_flags contains a bit mask of the following values:

Setting the extended (private) interface flags is a privileged operation.

SIOCGIFADDR, SIOCSIFADDR

Get or set the address of the device using ifr_addr. Setting the interface address is a privileged operation. For compatibility, only AF_INET addresses are accepted or returned.

SIOCGIFDSTADDR, SIOCSIFDSTADDR

Get or set the destination address of a point-to-point device using ifr_dstaddr. For compatibility, only AF_INET addresses are accepted or returned. Setting the destination address is a privileged operation.

SIOCGIFBRDADDR, SIOCSIFBRDADDR

Get or set the broadcast address for a device using ifr_brdaddr. For compatibility, only AF_INET addresses are accepted or returned. Setting the broadcast address is a privileged operation.

SIOCGIFNETMASK, SIOCSIFNETMASK

Get or set the network mask for a device using ifr_netmask. For compatibility, only AF_INET addresses are accepted or returned. Setting the network mask is a privileged operation.

SIOCGIFMETRIC, SIOCSIFMETRIC

Get or set the metric of the device using ifr_metric. This is currently not implemented; it sets ifr_metric to 0 if you attempt to read it and returns EOPNOTSUPP if you attempt to set it.

SIOCGIFMTU, SIOCSIFMTU

Get or set the MTU (Maximum Transfer Unit) of a device using ifr_mtu. Setting the MTU is a privileged operation. Setting the MTU to too small values may cause kernel crashes.

SIOCGIFHWADDR, SIOCSIFHWADDR

Get or set the hardware address of a device using ifr_hwaddr. The hardware address is specified in a struct sockaddr. sa_family contains the ARPHRD_* device type, sa_data the L2 hardware address starting from byte 0. Setting the hardware address is a privileged operation.

SIOCSIFHWBROADCAST

Set the hardware broadcast address of a device from ifr_hwaddr. This is a privileged operation.

SIOCGIFMAP, SIOCSIFMAP

Get or set the interface’s hardware parameters using ifr_map. Setting the parameters is a privileged operation.

If ifc_req is NULL, SIOCGIFCONF returns the necessary buffer size in bytes for receiving all available addresses in ifc_len. Otherwise, ifc_req contains a pointer to an array of ifreq structures to be filled with all currently active L3 interface addresses. ifc_len contains the size of the array in bytes. Within each ifreq structure, ifr_name will receive the interface name, and ifr_addr the address. The actual number of bytes transferred is returned in ifc_len.

If the size specified by ifc_len is insufficient to store all the addresses, the kernel will skip the exceeding ones and return success. There is no reliable way of detecting this condition once it has occurred. It is therefore recommended to either determine the necessary buffer size beforehand by calling SIOCGIFCONF with ifc_req set to NULL, or to retry the call with a bigger buffer whenever ifc_len upon return differs by less than sizeof(struct ifreq) from its original value.

If an error occurs accessing the ifconf or ifreq structures, EFAULT will be returned.

Most protocols support their own ioctls to configure protocol-specific interface options. See the protocol man pages for a description. For configuring IP addresses, see ip(7).

In addition, some devices support private ioctls. These are not described here.

NOTES

Strictly speaking, SIOCGIFCONF and the other ioctls that accept or return only AF_INET socket addresses, are IP-specific and belong in ip(7).

The names of interfaces with no addresses or that don’t have the IFF_RUNNING flag set can be found via /proc/net/dev.

Local IPv6 IP addresses can be found via /proc/net or via rtnetlink(7).

BUGS

glibc 2.1 is missing the ifr_newname macro in <net/if.h>. Add the following to your program as a workaround:

#ifndef ifr_newname
#define ifr_newname ifr_ifru.ifru_slave
#endif

SEE ALSO

COLOPHON

This page is part of release 4.00 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man−pages/.